Liquid crystal display device

ABSTRACT

An MVA mode liquid crystal display device is configured such that a liquid crystal layer including liquid crystal molecules having negative dielectric constant anisotropy is held between a first substrate and a second substrate. The liquid crystal display device includes a structural body which controls an alignment direction of the liquid crystal molecules in a manner to form a multi-domain in each of pixels. The structural body includes a first structural body which is disposed in a manner to overlap a light-blocking wiring line, and a second structural body which is disposed in a direction substantially perpendicular to the first structural body and is formed to be narrower than the first structural body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-320059, filed Dec. 11, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a liquid crystal displaydevice, and more particularly to a liquid crystal display device whichadopts a multi-domain vertical alignment mode.

2. Description of the Related Art

A liquid crystal display device has various features such as smallthickness, light weight and low power consumption, and is applied tovarious uses, e.g. OA equipment, information terminals, timepieces, andTVs. In particular, a liquid crystal display device comprising thin-filmtransistors (TFTs) including thin-film transistors (hereinafter “TFTs”)has high image quality performance and, therefore, it is widely used asa monitor of a portable TV, a computer, etc., which displays a greatdeal of information.

In recent years, with an increase in information amount, there has beenan increasing demand for higher definition of images and for a higherdisplay speed. The higher definition of images can be realized, forexample, by making finer the array structure which is composed of theabove-described TFTs. Of display modes of liquid crystal displaydevices, a vertical aligned nematic (VAN) mode has a higher responsespeed than a conventional twisted nematic (TN) mode. An additionalfeature of the VAN mode is that a rubbing process, which may lead to adefect such as an electrostatic breakage, can be made needless byvertical alignment.

In particular, a multi-domain VAN (MVA) is widely put to practical usesince the viewing angle can relatively easily be increased.

In the MVA mode, liquid crystal molecules are aligned in a plurality ofdirections when a voltage is applied to the liquid crystal layer, forexample, by means of mask rubbing, devices of pixel electrodestructures, or protrusions provided in pixels. Thereby, a multi-domainis formed, and an improvement in symmetry of viewing anglecharacteristics and suppression of an inversion phenomenon are realized.In addition, the viewing angle dependency of the retardation of theliquid crystal layer in the state in which the liquid crystal moleculesare vertically aligned, that is, in the black display mode, iscompensated by using a negative retardation plate. Thereby, the viewingangle dependency of the contrast ratio (CR) is improved. Furthermore, byapplying a biaxial retardation plate with an in-plane retardation to thenegative retardation plate, the viewing angle dependency of thepolarizer plate is also compensated, and still higher CR viewing anglecharacteristics are realized.

For example, patent document 1 (Jpn. Pat. Appln. KOKAI Publication No.H11-258606) discloses a technique relating to the MVA. Patent document 1discloses domain restriction means, such as a protrusion, a recess or aslit, as means for forming a multi-domain. In a concrete example, aprotrusion is provided on a counter-electrode, and neighboring pixelelectrodes on an array substrate are disposed at a predeterminedinterval or more, thereby realizing a multi-domain. Patent document 1describes that in the prior art the protrusion needs to have apredetermined width or more and a predetermined height or more from thestandpoint of alignment stability, and that if sufficient width andheight are not obtained, the alignment stability would deteriorate,leading to image quality degradation such as roughness and lowering inresponse speed.

On the other hand, since the protrusion is provided within the pixel,there occurs local light leak due to a stepped portion of the protrusionor a decrease in transmittance due to a voltage drop. Thus, the fact isthat the protrusion itself is a factor of degradation in image quality.Moreover, if the interval of pixel electrodes is to be increased, theopening ratio decreases and the transmittance lowers.

As has been described above, from the standpoint of the transmittanceand contrast, it is desirable that the size of the protrusion and theinterval of the pixel electrodes be as small as possible. In short, thesize of the protrusion and the interval of pixel electrodes aredetermined from the relationship of trade-off between the opticalcharacteristics and the alignment stability.

As other techniques for forming the multi-domain, there are knowntechniques disclosed in patent documents 2 to 4 (Jpn. Pat. Appln. KOKAIPublication No. 2004-205903, Jpn. Pat. Appln. KOKAI Publication No.2004-341487 and Jpn. Pat. Appln. KOKAI Publication No. 2007-041126).

In recent years, also in the field of displays for mobile terminals,microfabrication has been progressed to realize very high definition of300 ppi or more, and there is a strong demand for the capability ofdisplaying motion video. Although the optical characteristics, such astransmittance and contrast, are in a sufficiently tolerable level, theresponse time is not sufficient and there is a demand for improvement indisplay quality at the time of motion video display.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-described problems, and the object of the invention is to providea liquid crystal display device adopting a multi-domain verticalalignment mode, which can decrease a response time, while maintainingoptical characteristics in a tolerable level.

According to a first aspect of the present invention, there is provideda liquid crystal display device which is configured such that a liquidcrystal layer including liquid crystal molecules having negativedielectric constant anisotropy is held between a first substrate and asecond substrate, comprising: pixel electrodes which are disposed inassociation with a plurality of pixels which are arrayed in a matrix, inthe first substrate; a first alignment film which is disposed in amanner to cover the pixel electrodes and aligns the liquid crystalmolecules in a direction substantially perpendicular to the firstsubstrate; light-blocking wiring lines which are disposed in a manner tocross the pixel electrodes and are formed of a light-blocking,electrically conductive material; a counter-electrode which is disposedin common with the plurality of pixels, in the second substrate; asecond alignment film which is disposed in a manner to cover thecounter-electrode and aligns the liquid crystal molecules in a directionsubstantially perpendicular to the second substrate; and an insulativeprotrusion which controls an alignment direction of the liquid crystalmolecules in a manner to form a multi-domain in each of the pixels,wherein the protrusion includes a first protrusion which is disposed ina manner to overlap the light-blocking wiring line, and a secondprotrusion which is disposed in a direction substantially perpendicularto the first protrusion and is formed to be narrower than the firstprotrusion.

According to a second aspect of the present invention, there is provideda liquid crystal display device which is configured such that a liquidcrystal layer including liquid crystal molecules having negativedielectric constant anisotropy is held between a first substrate and asecond substrate, comprising: pixel electrodes which are disposed inassociation with a plurality of pixels which are arrayed in a matrix, inthe first substrate; a first alignment film which is disposed in amanner to cover the pixel electrodes and aligns the liquid crystalmolecules in a direction substantially perpendicular to the firstsubstrate; light-blocking wiring lines which are disposed in a manner tocross the pixel electrodes and are formed of a light-blocking,electrically conductive material; a counter-electrode which is disposedin common with the plurality of pixels, in the second substrate; asecond alignment film which is disposed in a manner to cover thecounter-electrode and aligns the liquid crystal molecules in a directionsubstantially perpendicular to the second substrate; and a slit portionwhich controls an alignment direction of the liquid crystal molecules ina manner to form a multi-domain in each of the pixels, and is formed inthe pixel electrode or the counter-electrode, wherein the slit portionincludes a first slit portion which is formed in a manner to overlap thelight-blocking wiring line, and a second slit portion which is disposedin a direction substantially perpendicular to the first slit portion andis formed to be narrower than the first slit portion.

The present invention can provide a liquid crystal display deviceadopting a multi-domain vertical alignment mode, which can decrease aresponse time, while maintaining optical characteristics in a tolerablelevel.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 schematically shows the structure of a liquid crystal displaydevice according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view that schematically shows the structureof the liquid crystal display device shown in FIG. 1;

FIG. 3 is a plan view for describing the positional relationship betweenpixels and structural bodies (protrusions) in a liquid crystal displaydevice according to concrete example 1;

FIG. 4 schematically shows the structure of one pixel in concreteexample 1;

FIG. 5 is a cross-sectional view of the liquid crystal display panel,taken along line A-A′ in FIG. 4;

FIG. 6 is a cross-sectional view of the liquid crystal display panel,taken along line B-B′ in FIG. 4;

FIG. 7 is a plan view for describing the positional relationship betweenpixels and structural bodies (protrusions) in a liquid crystal displaydevice according to concrete example 2;

FIG. 8 schematically shows the structure of one pixel in concreteexample 2;

FIG. 9 is a cross-sectional view of the liquid crystal display panel,taken along line A-A′ in FIG. 8;

FIG. 10 is a cross-sectional view of the liquid crystal display panel,taken along line B-B′ in FIG. 8;

FIG. 11 is a plan view for describing the positional relationshipbetween pixels and structural bodies (slit portions) in a liquid crystaldisplay device according to concrete example 3;

FIG. 12 schematically shows the structure of one pixel in concreteexample 3;

FIG. 13 is a cross-sectional view of the liquid crystal display panel,taken along line A-A′ in FIG. 12;

FIG. 14 is a cross-sectional view of the liquid crystal display panel,taken along line B-B′ in FIG. 12;

FIG. 15 is a table showing an evaluation result of the roughness ofimage quality in relation to pixel pitches;

FIG. 16 shows a modification of concrete example 2, and is across-sectional view of the liquid crystal display panel, taken alongline A-A′ in FIG. 8;

FIG. 17 shows the modification of concrete example 2, and is across-sectional view of the liquid crystal display panel, taken alongline B-B′ in FIG. 8;

FIG. 18 shows a modification of concrete example 3, and is across-sectional view of the liquid crystal display panel, taken alongline A-A′ in FIG. 12; and

FIG. 19 shows the modification of concrete example 3, and is across-sectional view of the liquid crystal display panel, taken alongline B-B′ in FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

A liquid crystal display device according to an embodiment of thepresent invention will now be described with reference to theaccompanying drawings. In this embodiment, a liquid crystal displaydevice, in which at least a part of each of pixels is composed as atransmissive display part that displays an image by selectively passingbacklight, is exemplified.

As is shown in FIG. 1 and FIG. 2, the liquid crystal display device isan active-matrix-type color liquid crystal device, which includes aliquid crystal display panel LPN. The liquid crystal display panel LPNis configured to include an array substrate (first substrate) AR, acounter-substrate (second substrate) CT which is disposed to be opposedto the array substrate AR, and a liquid crystal layer LQ which is heldbetween the array substrate AR and the counter-substrate CT.

In addition, the liquid crystal display device includes a first opticalelement OD1 which is provided on one of outer surfaces of the liquidcrystal display panel LPN (i.e. a surface of the array substrate AR,which is opposed to the other surface thereof that is in contact withthe liquid crystal layer LQ), and a second optical element OD2 which isprovided on the other outer surface of the liquid crystal display panelLPN (i.e. a surface of the counter-substrate CT, which is opposed to theother surface thereof that is in contact with the liquid crystal layerLQ). Further, the liquid crystal display device includes a backlightunit BL which illuminates the liquid crystal display panel LPN from thefirst optical element OD1 side.

The liquid crystal display panel LPN includes a display region DSP thatdisplays an image. The display region DSP is composed of a plurality ofpixels PX which are arrayed in a matrix of m×n.

The array substrate AR is formed by using an insulating substrate 10having light transmissivity, such as a glass plate or a quartz plate.Specifically, the array substrate AR includes, in the display regionDSP, an (m×n) number of pixel electrodes EP which are disposed in therespective pixels, an n-number of scanning lines Y (Y1 to Yn) which aredisposed in a manner to extend in the row direction of the pixelelectrodes EP, an m-number of signal lines X (X1 to Xm) which aredisposed in a manner to extend in the column direction of the pixelelectrodes EP, an (m×n) number of switching elements W (e.g. thin-filmtransistors) which are disposed in regions including intersectionsbetween the scanning lines Y and signal lines X in the respective pixelsPX, and storage capacitance lines AY which are disposed in a manner toextend in the row direction, like the scanning lines Y, and arecapacitive-coupled to the pixel electrodes EP so as to constitutestorage capacitances CS in parallel with liquid crystal capacitancesCLC.

The scanning lines Y and storage capacitance lines AY are disposedsubstantially in parallel, and may be formed of the same material. Thestorage capacitance lines AY are opposed to the pixel electrodes EP viaan insulation film such as an interlayer insulation film 16, and aredisposed in a manner to cross the plural pixel electrodes EP. The signallines X are disposed so as to cross, substantially at right angles, thescanning lines Y and storage capacitance lines AY via the interlayerinsulation film 16. These signal lines X, scanning lines Y and storagecapacitance lines AY are light-blocking wiring lines which are formed ofa light-blocking, electrically conductive material such as aluminum,molybdenum, tungsten or titanium.

Each of the switching elements W is, for instance, an n-channelthin-film transistor, and includes a semiconductor layer 12 which isdisposed on the insulating substrate 10. The semiconductor layer 12 canbe formed of, e.g. polysilicon or amorphous silicon. In this embodiment,the semiconductor layer 12 is formed of polysilicon. The semiconductorlayer 12 includes a source region 12S and a drain region 12D, betweenwhich a channel region 12C is interposed. The semiconductor layer 12 iscovered with a gate insulation film 14.

A gate electrode WG of the switching element W is connected to oneassociated scanning line Y (or formed integral with the scanning lineY), and is disposed, together with the scanning line Y and storagecapacitance line AY, on the gate insulation film 14. The gate electrodeWG, scanning line Y and storage capacitance line AY are covered with theinterlayer insulation film 16. The gate insulation film 14 andinterlayer insulation film 16 are formed of an inorganic material suchas silicon oxide or silicon nitride.

A source electrode WS and a drain electrode WD of the switching elementW are disposed on the interlayer insulation film 16 on both sides of thegate electrode WG. The source electrode WS is connected to oneassociated signal line X (or formed integral with the signal line X) andis put in contact with the source region 12S of the semiconductor layer12. The drain electrode WD is connected to one associated pixelelectrode EP (or formed integral with the pixel electrode EP) and is putin contact with the drain region 12D of the semiconductor layer 12. Thesource electrode WS, drain electrode WD and signal line X are coveredwith a protection insulation film 18. The protection insulation film 18is formed of, e.g. an organic material.

The pixel electrode EP is disposed on the protection insulation film 18and is electrically connected to the drain electrode WD via a contacthole which is formed in the organic insulation film 18. The pixelelectrode EP is formed of a light-transmissive electrically conductivematerial such as indium tin oxide (ITO) or indium zinc oxide (IZO). Thepixel electrode EP, which is associated with each pixel PX, is coveredwith a first alignment film 20.

On the other hand, the counter-substrate CT is formed by using alight-transmissive insulating substrate 30 such as a glass plate or aquartz plate. Specifically, the counter-substrate CT includes acounter-electrode ET in the display region DSP. The counter-electrode ETis disposed to be opposed to the pixel electrodes EP in association withthe plural pixels PX. The counter-electrode ET is formed of alight-transmissive electrically conductive material such as ITO. Thecounter-electrode ET is covered with a second alignment film 36.

The liquid crystal display device of a color display type includes acolor filter layer 34 which is provided on the inner surface of theliquid crystal display panel LPN in association with each pixel. In theexample shown in FIG. 2, the color filter layer 34 is provided on thecounter-substrate CT. The color filter layer 34 is formed of colorresins of a plurality of different colors, for example, the threeprimary colors of red, blue and green. The red color resin, blue colorresin and green color resin are disposed in association with a redpixel, a blue pixel and a green pixel, respectively.

The color filter layer 34 may be disposed on the array substrate ARside. In this case, the protection insulation film 18 of the arraysubstrate AR may be replaced with a color filter layer 34.

The respective pixels PX are partitioned by a black matrix (not shown).The black matrix is disposed to be opposed to wiring lines, such asscanning lines Y, signal lines X and switching elements W, which areprovided on the array substrate AR. In order to reduce the influence ofirregularities on the surface of the color filter layer 34, an overcoatlayer may be disposed between the color filter layer 34 and thecounter-electrode ET.

When the counter-substrate CT and the above-described array substrate ARare disposed such that their first alignment film 20 and secondalignment film 36 are opposed, a predetermined gap is provided byspacers (e.g. columnar spacers which are formed of resin material so asto be integral with one of the substrates) not shown, which are disposedbetween both alignment films 20 and 36. The liquid crystal layer LQ iscomposed of a liquid crystal composition including liquid crystalmolecules 40, which is sealed in the gap between the first alignmentfilm 20 of the array substrate AR and the second alignment film 36 ofthe counter-substrate CT. The liquid crystal molecules 40 have negativedielectric constant anisotropy.

The first alignment film 20 and second alignment film 36 have suchcharacteristics as to align the liquid crystal molecules 40substantially perpendicular to the insulating substrate 10 (or arraysubstrate AR) and the insulating substrate 30 (or counter-substrate CT).The material of the first alignment film 20 and second alignment film 36is not basically limited if the first alignment film 20 and secondalignment film 36 are formed of light-transmissive thin films havingvertical alignment properties.

In a driving circuit region DCT in the vicinity of the display regionDSP of the array substrate AR, the liquid crystal display deviceincludes at least a part of a scanning line driver YD which is connectedto the n-number of scanning lines Y and at least a part of a signal linedriver XD which is connected to the m-number of signal lines X. In thiscase, the scanning line driver YD and signal line driver XD may include,like the switching elements W, thin-film transistors includingpolysilicon.

The scanning line driver YD successively supplies scanning signals(driving signals) to the n-number of scanning lines Y on the basis ofthe control by a controller CNT. The signal line driver XD supplies,under the control of the controller CNT, video signals (driving signals)to the m-number of signal lines X at a timing when the switchingelements W of each row are turned on by the scanning signal. Thereby,the pixel electrodes EP in each row are set at pixel potentialscorresponding to the video signals that are supplied via the associatedswitching elements W.

The first optical element OD1 and second optical element OD2 include atleast polarizers, respectively. The polarizers are disposed such thattheir absorption axes intersect at right angles. Each of the firstoptical element OD1 and second optical element OD2 may include aretardation plate which imparts a proper retardation to transmissivelight. For example, in a display mode which makes use of circularpolarization, each of the first optical element OD1 and second opticalelement OD2 includes, in addition to the polarizer, a retardation platewhich imparts a λ/4 retardation to transmissive light.

In the present embodiment, in a case where no voltage is applied betweenthe pixel electrode EP and the counter-electrode ET or a voltage lowerthan a threshold voltage is applied between the pixel electrode EP andthe counter-electrode ET, the liquid crystal molecules are alignedsubstantially parallel to the normal direction of the liquid crystaldisplay panel LPN (i.e. the normal direction of the array substrate ARand counter-substrate CT) by the alignment control by the alignmentfilms 20 and 36.

In this state, backlight that has passed through the first opticalelement OD1 travels through the liquid crystal layer LQ, and is thenabsorbed by the second optical element OD2. Thus, black display iseffected.

On the other hand, in a case where a voltage of the threshold value ormore is applied between the pixel electrode EP and the counter-electrodeET, the liquid crystal molecules are aligned oblique or substantiallyperpendicular to the normal direction of the liquid crystal displaypanel LPN (i.e. substantially parallel to the major surfaces of thearray substrate AR and counter-substrate CT).

In this state, backlight that has passed through the first opticalelement OD1 travels through the liquid crystal layer LQ, and then passesthrough the second optical element OD2. Thus, white display is effected.

In this manner, the vertical alignment mode is realized.

In the meantime, the liquid crystal display device includes structuralbodies which control the alignment direction of the liquid crystalmolecules 40 so as to form multi-domains in the respective pixels PX.

In the present invention, in order to increase the region with aninclination of electric field, in addition to the function ofrestricting the direction of inclination of liquid crystal molecules 40,it was found, on the basis of various alignment simulations andevaluation results of trial models of panels, that the response time canbe decreased while the optical characteristics, such as thetransmittance and contrast ratio, are maintained at tolerable levels.Based on this finding, it is possible to realize a liquid crystaldisplay device with a high display quality of motion video, wherein evenin the case where the same liquid crystal material as in the prior artis used and the same cell gap as in the prior art is set in ahigh-definition panel of 300 ppi or more, the response time between graylevels at a time of intermediate gray level display can be reduced to ½to ⅓ of that in the prior art.

Concrete examples of the liquid crystal display device including thestructural body will now be described in detail.

In each of the concrete examples below, the liquid crystal displaydevice is constructed as a VGA color active-matrix liquid crystaldisplay device having a diagonal screen size of 2.4 inches for mobileterminals, and having RGB pixels, the number of which is 640(vertical)×320 (horizontal). The resolution of the display device is 332ppi (pixels/inch). The size of one pixel is 75 μm in the longitudinaldirection (i.e. the column direction) and 25 μm in the transversedirection (i.e. the row direction). Thus, the pixel electrode EP of eachpixel is formed in a substantially rectangular direction having a longside in the column direction and a short side in the row direction.

In the present embodiment, the interval of repetition of each pixel inthe transverse direction (i.e. the length in the row direction of eachpixel) is referred to as a pixel pitch.

In each of the concrete examples, the interval 1 p of neighboring pixelelectrodes is about 8 μm, and the cell gap d (i.e. the thickness of theliquid crystal layer held between the first alignment film and secondalignment film) is 3 μm. As the material of the liquid crystal layer LQ,use was made of a fluorine-based liquid crystal material (manufacturedby Merck & Co. Inc.) having a refractive index anisotropy Δn of 0.09, adielectric constant anisotropy Δ ∈ of −5 in the n-type, and a rotationalviscosity coefficient of 100 mPa·S.

CONCRETE EXAMPLE 1

Concrete example 1 shown in FIG. 3 adopts a method in which one pixel PXis divided into two parts, and includes, as structural bodies,protrusions CC on the counter-substrate side. The protrusion extends inthe row direction through a substantially central part of the pixelelectrode EP so as to divide each pixel into two parts, and theprotrusion CC is disposed so as to cross each of the pixel electrodes EPdisposed in plural pixels.

The protrusion CC having the stripe shape has a width (i.e. the lengthin the column direction) of, e.g. 10 μm and a height of, e.g. 1.5 μm.The length (i.e. the length in the row direction) of the protrusion CCis equal to or greater than the transverse length of the pixel. In thisexample, the protrusion CC has a length of 25 μm or more. The protrusionCC was formed of an acrylic photosensitive resin material.

FIG. 4 schematically shows the structure of one pixel. FIG. 5 is across-sectional view of the liquid crystal display panel, taken alongline A-A′ in FIG. 4, showing the state in which alignment of liquidcrystal molecules 40 propagates when a voltage of a threshold value ormore is applied between the pixel electrode EP and the counter-electrodeET. FIG. 6 is a cross-sectional view of the liquid crystal displaypanel, taken along line B-B′ in FIG. 4, showing the state in whichalignment of liquid crystal molecules 40 propagates when a voltage of athreshold value or more is applied between the pixel electrode EP andthe counter-electrode ET. FIG. 3 to FIG. 6 show only main parts whichare necessary for description.

Specifically, in the counter-substrate CT, the protrusion CC is disposedon the counter-electrode ET, and is covered with a second alignment film36 (not shown). The protrusion CC has a semicircular cross-sectionalshape. The array substrate AR includes the pixel electrode EP in eachpixel, and a part of the pixel electrode EP is opposed to the protrusionCC.

As shown in FIG. 5 and FIG. 6, in a case where a voltage of a thresholdvalue or more is applied between the pixel electrode EP andcounter-electrode ET, an electric field (electric force lines) E isgenerated between the pixel electrode EP and counter-electrode ET,except for a part where the insulative protrusion CC is disposed. Theliquid crystal molecules 40 are aligned and controlled in response tosuch an electric field E.

In particular, as regards the column direction, as shown in FIG. 5, anelectric field E in the normal direction of the liquid crystal displaypanel is generated in the region which is sufficiently away from theprotrusion CC. On the other hand, an electric field E, which is obliqueto the normal direction of the liquid crystal display panel in a mannerto avoid the protrusion CC, is generated at the region where theprotrusion CC is disposed and the neighborhood of this region.

At this time, the liquid crystal molecules 40 are aligned so as to beinclined to the normal direction by the influence of the obliqueelectric field E. The direction of alignment of liquid crystal molecules40 depends on the direction of the electric field E with a relativelygreat inclination, which is generated in the vicinity of the protrusionCC. Specifically, the liquid crystal molecules 40 begin to incline fromthe vicinity of the protrusion CC, and the alignment of the liquidcrystal gradually propagates in a direction away from this region as abase point (i.e. in a direction toward the region where the inclinationof the electric field E is small).

As regards the row direction, as shown in FIG. 6, an electric field E,which is inclined to the normal direction of the liquid crystal displaypanel in a manner to avoid the gap between neighboring pixel electrodes,is generated in the vicinity of end portions of the pixel electrode EP(i.e. in the vicinity of the long side of the pixel electrode).

At this time, the direction of alignment of liquid crystal molecules 40depends on the direction of the electric field E with a relatively greatinclination, which is generated in the vicinity of the end portions ofthe pixel electrode EP. Specifically, the liquid crystal molecules 40begin to incline from the vicinity of the end portion of the pixelelectrode EP, and the alignment of the liquid crystal graduallypropagates in a direction away from this region as a base point.

The above-described propagation time of the liquid crystal alignment inthe row direction and column direction causes a delay in response time.

Hence, as the distance from the protrusion or the end portion of thepixel is greater (i.e. as the region with no inclination of the electricfield is greater), the response time is longer. Conversely, as thedistance from the protrusion or the end portion of the pixel is smaller(i.e. as the region with no inclination of the electric field issmaller), the response time is shorter. However, if the number ofprotrusions CC or pixel end portions is increased, the area (apertureratio) that contributes to display becomes smaller, and the opticalcharacteristics, such as the transmittance and contrast ratio,deteriorate. As described above, there is a trade-off between theresponse time and the optical characteristics, and it is difficult tomake them compatible.

A liquid crystal cell, which was manufactured on the basis of concreteexample 1 that has been described above with reference to FIG. 3 to FIG.6, was assembled as a module, and the optical characteristics thereofwere measured. The transmittance of the liquid crystal cell was 5%, andthe contrast ratio was 700. The response time was 170 msec, under thecondition that the slowest response time between gray levels wasmeasured when eight gray levels were displayed. When motion video wasdisplayed, so-called “trailing” with a visible after-image wasconfirmed, and the response time was insufficient.

CONCRETE EXAMPLE 2

FIG. 7 is a plan view showing a layout of concrete example 2. FIG. 8schematically shows the structure of one pixel. FIG. 9 is across-sectional view of the liquid crystal display panel, taken alongline A-A′ in FIG. 8, showing the state in which alignment of liquidcrystal molecules 40 propagates when a voltage of a threshold value ormore is applied between the pixel electrode EP and the counter-electrodeET. FIG. 10 is a cross-sectional view of the liquid crystal displaypanel, taken along line B-B′ in FIG. 8, showing the state in whichalignment of liquid crystal molecules 40 propagates when a voltage of athreshold value or more is applied between the pixel electrode EP andthe counter-electrode ET. FIG. 7 to FIG. 10 show only main parts whichare necessary for description.

Concrete example 2 shown in FIG. 7 corresponds to one of embodiments ofthe invention. Concrete example 2 includes, as a structural body CB, aprotrusion (first protrusion) CC1 corresponding to a first structuralbody and a protrusion (second protrusion) CC2 corresponding to a secondstructural body.

The protrusion CC1 has a stripe shape, like the protrusion CC ofconcrete example 1. The protrusion CC1 extends in the row directionthrough a substantially central part of the pixel electrode EP so as todivide each pixel into two parts, and the protrusion CC1 is disposed incommon with plural pixels PX so as to cross the pixel electrode EP ofeach pixel. The protrusion CC1 is disposed so as to overlaplight-blocking wiring. In this example, a storage capacitance line AY isdisposed, as the light-blocking wiring line, so as to cross the pixelelectrode EP, and the protrusion CC1 is disposed in a manner to overlapthe storage capacitance line AY.

In this manner, the protrusion CC1 is disposed on that part within thepixel PX, which does not contribute to display. Specifically, theregion, where local light leak occurs due to a stepped portion of theprotrusion CC1 or a decrease in transmittance occurs due to a voltagedrop, is configured to overlap the light-blocking wiring line. On theother hand, the protrusion CC1 can be formed with a maximum size fromthe standpoint of alignment stability. Thus, no decrease occurs inaperture ratio due to the provision of the protrusion CC1, and thealignment stability can be secured.

This protrusion CC1, like concrete example 1, has a width (i.e. thelength in the column direction) of, e.g. 10 μm and a height of, e.g. 1.5μm. The protrusion CC1 has a length (i.e. the length in the rowdirection) of 25 μm or more.

The protrusion CC2, like the protrusion CC1, has a stripe shape and isdisposed in a manner to intersect at right angles with the protrusionCC1 within the pixel PX. Specifically, the protrusion CC2 extends in thecolumn direction through a substantially central portion of the pixelelectrode EP. In other words, the protrusion CC1 and protrusion CC2 aredisposed so as to cross at a substantially central portion on the pixelelectrode EP.

Thereby, on the pixel electrode EP, four substantially uniform areas,which are divided by the structural body CB, are formed. Compared toconcrete example 1, the region where the inclined electric field isformed, which becomes the base point of liquid crystal alignment, can beincreased. In short, the response time can be decreased.

The protrusion CC2 is formed to be narrower than the protrusion CC1.Specifically, the width of the protrusion CC1 is set at 10 μm, and thewidth of the protrusion CC2 (i.e. the length in the row direction) isset at 6 μm. Like the protrusion CC1, the height of the protrusion CC2is set at 1.5 μm.

Parts of the protrusion CC2 are disposed on those parts within the pixelPX, which contribute to display. Thus, the protrusion CC2 is formed tohave a minimum size in consideration of the alignment stability.Thereby, a decrease in aperture ratio can be minimized.

In concrete example 2, the protrusion CC2 extends substantially parallelto the long side of the pixel electrode EP and is formed to have ashorter length than the long side of the pixel electrode EP in onepixel. Specifically, the length in the column direction of theprotrusion CC2 is less than the longitudinal length of the pixel and isset at 50 μm in this example.

In addition, both ends of the protrusion CC2 do not reach the shortsides of the pixel electrode EP, and regions, where the pixel electrodeEP is opposed to the counter-electrode ET, are formed between both endsof the protrusion CC2 and the short sides of the pixel electrodes EP.

It is desirable that the protrusions CC1 and CC2 be formed of alight-transmissive insulating material. For example, the protrusions CC1and CC2 are formed by using an acrylic photosensitive resin material.The protrusions CC1 and CC2 can be formed at the same time by a singlepatterning step after the film of the photosensitive resin material isformed.

Specifically, in the counter-substrate CT, the protrusion CC1 andprotrusion CC2 are disposed on the counter-electrode ET, and are coveredwith a second alignment film 36 (not shown). Each of the protrusions CC1and CC2 has a semicircular cross-sectional shape. The array substrate ARincludes the pixel electrode EP in each pixel, and a part of the pixelelectrode EP is opposed to the protrusions CC1 and CC2.

As shown in FIG. 9 and FIG. 10, in a case where a voltage of a thresholdvalue or more is applied between the pixel electrode EP andcounter-electrode ET, an electric field (electric force lines) E isgenerated between the pixel electrode EP and counter-electrode ET,except for a part where the protrusions CC1 and CC2 are disposed. Theliquid crystal molecules 40 are aligned and controlled in response tosuch an electric field E.

As regards the column direction, as has been described with reference toFIG. 5, an electric field E, which is inclined to the normal directionof the liquid crystal display panel in a manner to avoid the protrusionCC1, is generated at the region where the protrusion CC1 is disposed andthe neighborhood of this region. In addition, as shown in FIG. 9, sincethe protrusion CC2 extends in the column direction, an electric field E,which is inclined to the normal direction of the liquid crystal displaypanel in a manner to avoid the protrusion CC2, is generated at theregion where the protrusion CC2 is disposed and the neighborhood of thisregion.

In particular, since the region, where the pixel electrode EP andcounter-electrode ET are opposed, is formed between both ends of theprotrusion CC2 and the short sides of the pixel electrode EP, aninclined electric field toward this region is formed in a manner toavoid the protrusion CC2.

Thus, the liquid crystal molecules 40 begin to incline from the vicinityof the protrusion CC1 and the vicinity of the short side of the pixelelectrode EP, and the alignment of the liquid crystal graduallypropagates in a direction away from these regions as base points (i.e.in a direction toward the region where the inclination of the electricfield E is small). In concrete example 1, the liquid crystal alignmentpropagates only in one direction from the vicinity of the protrusion. Bycontrast, in concrete example 2, with the provision of the protrusionCC2, since the inclined electric field is generated in a manner to avoidthe protrusion CC2, the liquid crystal alignment propagates in twodirections from the vicinity of the protrusion CC1 and the vicinity ofthe short side of the pixel electrode EP.

As regards the row direction, as shown in FIG. 10, an electric field E,which is inclined to the normal direction of the liquid crystal displaypanel in a manner to avoid the protrusion CC2, is generated at the partwhere the protrusion CC2 is disposed and in the vicinity of this region.At the same time, an electric field E, which is inclined to the normaldirection of the liquid crystal display panel in a manner to avoid thegap between neighboring pixel electrodes, is generated in the vicinityof the end portion of the pixel electrode EP (i.e. in the vicinity ofthe long side of the pixel electrode).

Thus, the liquid crystal molecules 40 begin to incline from the vicinityof the protrusion CC2 and the vicinity of the long side of the pixelelectrode EP, and the alignment of the liquid crystal graduallypropagates in a direction away from these regions as base points. Inconcrete example 1, the liquid crystal alignment propagates only in onedirection from the vicinity of the long side of the pixel electrode EP.By contrast, in concrete example 2, the liquid crystal alignmentpropagates in two directions from the vicinity of the protrusion CC2 andthe vicinity of the long side of the pixel electrode EP.

According to concrete example 2, the propagation time of liquid crystalalignment in the row direction and column direction can be made shorterthan in concrete example 1.

A liquid crystal cell, which was manufactured on the basis of concreteexample 2 that has been described above with reference to FIG. 7 to 10,was assembled as a module, and the optical characteristics thereof weremeasured. The transmittance of the liquid crystal cell was 4.6%, and thecontrast ratio was 500. It was confirmed that the transmittance andcontrast ratio were kept at sufficiently tolerable levels.

The response time was 60 msec, under the condition that the slowestresponse time between gray levels was measured when eight gray levelswere displayed, and a sufficient improvement in response speed wasconfirmed. When motion video was displayed, no “trailing” was confirmed,and a higher display quality with higher smoothness than concreteexample 1 was obtained.

In the above-described concrete example 2, the protrusions CC1 and CC2,which constitute the structural body CB, are disposed on thecounter-substrate CT. Alternatively, as shown in FIG. 16 and FIG. 17,the protrusions CC1 and CC2 may be disposed on the pixel electrode EP inthe array substrate AR. Besides, one of the protrusions CC1 and CC2 maybe disposed on the array substrate AR, and the other may be disposed onthe counter-substrate CT. In this manner, no matter whether theprotrusions CC1 and CC2 are disposed on the counter-substrate CT or onthe array substrate AR, the same advantageous effects can be obtained.

CONCRETE EXAMPLE 3

FIG. 11 is a plan view showing a layout of concrete example 3. FIG. 12schematically shows the structure of one pixel. FIG. 13 is across-sectional view of the liquid crystal display panel, taken alongline A-A′ in FIG. 12, and FIG. 14 is a cross-sectional view of theliquid crystal display panel, taken along line B-B′ in FIG. 12. FIG. 11to FIG. 14 show only main parts which are necessary for description.

Concrete example 3 shown in FIG. 11 corresponds to one of embodiments ofthe invention. Concrete example 3 includes, as a structural body CB, aslit portion (first slit portion) SL1 corresponding to a firststructural body and a slit portion (second slit portion) SL2corresponding to a second structural body.

The slit portion SL1 has a stripe shape, like the protrusion CC ofconcrete example 1. The slit portion SL1 extends in the row directionthrough a substantially central part of the pixel electrode EP so as todivide each pixel into two parts, and the slit portion SL1 is disposedin common with plural pixels PX so as to cross the pixel electrode EP ofeach pixel. The slit portion SL1 is disposed so as to overlap thestorage capacitance line AY that is the light-blocking wiring line.

This slit portion SL1, like concrete example 1, has a width (i.e. thelength in the column direction) of, e.g. 10 μm and a length (i.e. thelength in the row direction) of 25 μm or more.

The slit portion SL2, like the slit portion SL1, has a stripe shape andis disposed in a manner to intersect at right angles with the slitportion SL1 within the pixel PX. Specifically, the slit portion SL2extends in the column direction through a substantially central portionof the pixel electrode EP. In other words, the slit portion SL1 and slitportion SL2 are disposed so as to cross at a substantially centralportion on the pixel electrode EP.

The slit portion SL2 is formed to be narrower than the slit portion SL1.Specifically, the width of the slit portion SL1 is set at 10 μm, and thewidth of the slit portion SL2 (i.e. the length in the row direction) isset at 6 μm.

In concrete example 3, the slit portion SL2 extends substantiallyparallel to the long side of the pixel electrode EP and is formed tohave a shorter length than the long side of the pixel electrode EP inone pixel. Specifically, the length in the column direction of the slitportion SL2 is less than the longitudinal length of the pixel and is setat 50 μm in this example.

In addition, both ends of the slit portion SL2 do not reach the shortsides of the pixel electrode EP, and regions, where the pixel electrodeEP is opposed to the counter-electrode ET, are formed between both endsof the slit portion SL2 and the short sides of the pixel electrodes EP.

The slit portions SL1 and SL2 are formed in the counter-electrode ET.The slit portions SL1 and SL2 can be formed at the same time by a stepof patterning the counter-electrode ET. The array substrate AR includesthe pixel electrode EP in each pixel, and a part of the pixel electrodeEP is opposed to the slit portions SL1 and SL2.

In concrete example 3, too, on the pixel electrode EP, foursubstantially uniform areas, which are divided by the structural bodyCB, are formed. Compared to concrete example 1, the region where theinclined electric field is formed, which becomes the base point ofliquid crystal alignment, can be increased. According to concreteexample 3, like concrete example 2, the propagation time of liquidcrystal alignment in the row direction and column direction can be madeshorter than in concrete example 1. In short, the response time can bedecreased.

A liquid crystal cell, which was manufactured on the basis of concreteexample 3 that has been described above with reference to FIG. 11 to 14,was assembled as a module, and the optical characteristics thereof weremeasured. The transmittance of the liquid crystal cell was 5.0%, and thecontrast ratio was 900. It was confirmed that better opticalcharacteristics are obtainable than in concrete examples 1 and 2.

The response time was 70 msec, under the condition that the slowestresponse time between gray levels was measured when eight gray levelswere displayed, and a sufficient improvement in response speed wasconfirmed. When motion video was displayed, no “trailing” was confirmed,and a higher display quality with higher smoothness than concreteexample 1 was obtained.

In the above-described concrete example 3, the slit portions SL1 andSL2, which constitute the structural body CB, are formed in thecounter-electrode ET. Alternatively, as shown in FIG. 18 and FIG. 19,the slit portions SL1 and SL2 may be formed in the pixel electrode EP inthe array substrate AR. One of the slit portions SL1 and SL2 may beformed in the pixel electrode EP, and the other may be formed in thecounter-electrode ET. In this manner, no matter whether the slitportions SL1 and SL2 are formed in the counter-electrode ET or in thepixel electrode EP, the same advantageous effects can be obtained.

CONCRETE EXAMPLE 4

Concrete example 4 corresponds to one of embodiments of the invention.Like concrete example 3, concrete example 4 includes, as a structuralbody CB, a slit portion (first slit portion) SL1 corresponding to afirst structural body and a slit portion (second slit portion) SL2corresponding to a second structural body (depiction of slit portionsSL1 and SL2 is omitted). The difference between concrete example 4 andconcrete example 3 is that the width of the slit portion SL2 is madeequal to the width of the slit portion SL1, and is set at 10 μm.

A liquid crystal cell, which was manufactured on the basis of concreteexample 4, was assembled as a module, and the optical characteristicsthereof were measured. The transmittance of the liquid crystal cell was4.8%, and the contrast ratio was 850. It was confirmed that opticalcharacteristics, which are equal to or better than those in concreteexamples 1 and 2, are obtainable.

The response time was 65 msec, under the condition that the slowestresponse time between gray levels was measured when eight gray levelswere displayed, and a sufficient improvement in response speed wasconfirmed. When motion video was displayed, no “trailing” was confirmed,and a higher display quality with higher smoothness than concreteexample 1 was obtained.

CONCRETE EXAMPLE 5

Concrete example 5 corresponds to one of embodiments of the invention.Like concrete example 3, concrete example 5 includes, as a structuralbody CB, a slit portion (first slit portion) SL1 corresponding to afirst structural body and a slit portion (second slit portion) SL2corresponding to a second structural body (depiction of slit portionsSL1 and SL2 is omitted). The difference between concrete example 5 andconcrete example 3 is that the width of the slit portion SL2 is madegreater than the width of the slit portion SL1, and is set at 15 μm.

A liquid crystal cell, which was manufactured on the basis of concreteexample 5, was assembled as a module, and the optical characteristicsthereof were measured. The transmittance of the liquid crystal cell was4.0%, and the contrast ratio was 750. It was confirmed that with theincrease of the width of the slit portion SL2 which is disposed in theregion that contributes to display, although the transmittance becomeslower than in concrete example 1, the contrast ratio becomes higher thanin concrete examples 1 and 2, and good optical characteristics areobtainable.

The response time was 55 msec, under the condition that the slowestresponse time between gray levels was measured when eight gray levelswere displayed, and a sufficient improvement in response speed wasconfirmed. When motion video was displayed, no “trailing” was confirmed,and a higher display quality with higher smoothness than concreteexample 1 was obtained.

From the result of the comparison between the respective concreteexamples as described above, it is found that as the second structuralbody which is adopted in order to increase the region where the electricfield is mainly inclined, the slit, rather than the protrusion, iseffective in maintaining the optical characteristics, such as thetransmittance and contrast ratio, at tolerable levels. The reason forthis is that in the case where the second structural body is formed ofthe insulative protrusion, the alignment of liquid crystal molecules isalready inclined at the time of non-application of voltage due to theinfluence of the stepped edge portions of the protrusion, and light leakoccurs.

In the case where the second structural body is formed of the slitportion, if the area of the slit portion is increased, the response timetends to be shorter, but the transmittance lowers. Thus, it is desirablethat the width of the second structural body be not greatly increasedand be set to be equal to or less than the width of the first structuralbody.

Preferably, the pixel pitch should be set at 50 μm or less. It is thuseffective to apply the present invention to a small-sized,high-definition liquid crystal display device. In the case where thepixel pitch is large, the size of the pixel electrode EP is large.Hence, even if the structural body is disposed, the effect ofimprovement of the response speed is not obtained.

For example, as regards the structure of concrete example 1, theroughness of the image quality, relative to the pixel pitch, wasevaluated, and a result shown in FIG. 15 was obtained. According to thisresult, when the pixel pitch was 50 μm or less, almost no roughness wasvisually recognized, and display with good image quality was effected.When the pixel pitch was greater than 50 μm, roughness was recognized.

As has been described above, in the present embodiment, in addition tothe first structural body (the protrusion or the slit portion of theelectrode) for mainly restricting the direction of inclination of liquidcrystal molecules, there is further provided the second structural body(the protrusion or the slit portion of the electrode) for inclining theelectric field and decreasing the time (i.e. response time) ofinclination of the liquid crystal.

According to the present embodiment, there can be provided a liquidcrystal display device of high definition of 200 ppi or more, inparticular, about 300 to 400 ppi, which has a high screen displayquality, wherein the response time can be decreased without degradingoptical characteristics, and motion video can be viewed withoutunnaturalness.

The present invention is not limited directly to the above-describedembodiments. In practice, the structural elements can be modified andembodied without departing from the spirit of the invention. Variousinventions can be made by properly combining the structural elementsdisclosed in the embodiments. For example, some structural elements maybe omitted from all the structural elements disclosed in theembodiments. Furthermore, structural elements in different embodimentsmay properly be combined.

The above-described embodiments relate to the cases using transmissiveliquid crystal display panels. The invention, however, is alsoapplicable to transflective liquid crystal display devices wherein eachof the pixels includes a transmissive display part and a reflectivedisplay part.

In addition, the above-described embodiments relate to the cases inwhich the storage capacitance line, which is disposed in a manner tocross a substantially central part of the pixel electrode, is alight-blocking wiring line. However, in the structure in which thescanning line is disposed in a manner to cross a substantially centralpart of the pixel electrode, the scanning line, in place of the storagecapacitance line, functions as the light-blocking wiring line.

Furthermore, in a concrete example, the insulative protrusion and theslit portion that is formed in the electrode may be combined as thestructural body CB. Specifically, one of the first structural body andthe second structural body may be a protrusion which is disposed on thearray substrate or counter-substrate, and the other may be a slitportion which is formed in the counter-electrode or pixel electrode.

1. A liquid crystal display device which is configured such that aliquid crystal layer including liquid crystal molecules having negativedielectric constant anisotropy is held between a first substrate and asecond substrate, comprising: pixel electrodes which are disposed inassociation with a plurality of pixels which are arrayed in a matrix, inthe first substrate; a first alignment film which covers the pixelelectrodes and aligns the liquid crystal molecules in a directionsubstantially perpendicular to the first substrate; light-blockingwiring lines which cross the pixel electrodes and are formed of alight-blocking, electrically conductive material; a counter-electrodewhich is disposed in common with the plurality of pixels, in the secondsubstrate; a second alignment film which covers the counter-electrodeand aligns the liquid crystal molecules in a direction substantiallyperpendicular to the second substrate; and a slit portion which controlsan alignment direction of the liquid crystal molecules in a manner toform a multi-domain in each of the pixels, and is formed in the pixelelectrode or the counter-electrode, wherein the slit portion includes afirst slit portion which extends parallel to the light-blocking wiringline and overlaps the light-blocking wiring line, and a second slitportion which is substantially perpendicular to the first slit portion,extends parallel to a long side of the pixel electrode, is shorter thanthe long side of the pixel electrode, and is narrower than the firstslit portion, wherein the first slit portion and the second slit portioncross at a substantially central part on the pixel electrode, andwherein the first slit portion is formed in the counter-electrode, andcrosses the pixel electrodes disposed on the plurality of pixels.
 2. Theliquid crystal display device according to claim 1, wherein thelight-blocking wiring line is a scanning line or a storage capacitanceline, which extends in a row direction of the pixels.
 3. The liquidcrystal display device according to claim 1, wherein a pixel pitch is 50μm or less.
 4. The liquid crystal display device according to claim 1,wherein regions where the pixel electrode is opposed to thecounter-electrode include regions formed between both ends of the secondslit portion and short sides of the pixel electrode.
 5. A liquid crystaldisplay device which is configured such that a liquid crystal layerincluding liquid crystal molecules having negative dielectric constantanisotropy is held between a first substrate and a second substrate, theliquid crystal display device comprising: a pixel electrode which isdisposed in the first substrate, the pixel electrode including a pair ofshort sides which extend in a first direction and a pair of long sideswhich extend in a second direction crossing the first direction; a firstalignment film which covers the pixel electrode and aligns the liquidcrystal molecules in a direction perpendicular to the first substrate; alight-blocking wiring line which extends in the first direction, crossesthe pixel electrode and is formed of a light-blocking, electricallyconductive material; a counter-electrode which is disposed in the secondsubstrate, the counter-electrode including a single first slit portionwhich extends in the first direction through a central part of the pixelelectrode, crosses the pair of long sides, and overlaps thelight-blocking wiring line, and the counter-electrode further includinga single second slit portion which extends in the second direction,crosses the first slit portion at the central part of the pixelelectrode, is shorter than the pair of long sides, and is narrower thanthe first slit portion; and a second alignment film which covers thecounter-electrode and aligns the liquid crystal molecules in a directionperpendicular to the second substrate.
 6. The liquid crystal displaydevice according to claim 5, wherein the light-blocking wiring line is ascanning line or a storage capacitance line.
 7. The liquid crystaldisplay device according to claim 5, wherein a pixel pitch is 50 μm orless.
 8. The liquid crystal display device according to claim 5, whereinregions where the pixel electrode is opposed to the counter-electrodeinclude regions formed between both ends of the second slit portion andshort sides of the pixel electrode.